1. Technical Field
This invention relates generally to the field of water quality analysis and geochemical prospecting, and more specifically to an in-situ sampler for collecting suspended stream sediment over extended time periods.
2. Background Art
Over the years a variety of samplers and procedures have been developed and used for sampling suspended and bottom sediment. In general, the requisites for sampling suspended or fluvial sediment are different from those for sampling bottom sediment.
Suspended sediment in streams is sampled for a variety of purposes. In general, the intent is to supply samples for analyses to provide information on the quantity, i.e. concentration, and on the physical and chemical characteristics of the suspended sediment. Sorptive characteristics of suspended sediments have been recognized as an important process in the transport of natural and anthropogenic trace constituents. Suspended sediments have been used extensively in geochemical mineral exploration. They are also becoming increasingly recognized as important transporters of trace organic and inorganic contaminents in streams, lakes and marine environments.
Prior art suspended sediment samplers can be categorized into three classes--integrating samplers, instantaneous samplers and pumping samplers. Integrating samplers accumulate a water-sediment mixture over a period of time by withdrawing water and associated suspended sediment from the ambient flow through a relatively small nozzle. Instantaneous or grab samplers essentially trap a volume of the water-sediment mixture by instantaneously closing off the ends of a flow-through chamber. Pumping samplers withdraw a mixture of water and suspended sediment through an intake by a pumping action. Generally, passive integrating samplers are preferred because they obtain a water-sediment mixture from a long filament of flow, can sample at more than one point, and require no energy input or complicated velocity sensing and adjusting apparatus.
In the past, a variety of hand-held and cable and reel integrated samplers have been used to assess suspended sediment concentrations in streams. These samplers were generally designed to sample relatively small quantities of water, usually less than one liter and therefore have limited application for environmental and geochemical exploration sampling.
Various filtering apparati have been used to separate suspended sediments which rely on collection of a water sample and then separating the suspended fraction by some mechanical process. Commonly, water samples are collected and either filtered at the site or the suspended material is separated at the laboratory. In either case, whole water samples are collected within short term periods and therefore reflect instantaneous or short term stream events or episodes. Continuous sampling pumps, coupled to an on-site centrifuge are able to sample large volumes of water for extended periods. This approach, however, requires an electrical source which limits application to relatively accessible areas, and is also personnel intensive requiring continuous monitoring.